1. Field of the Invention
The invention relates generally to the field of excavation of subterranean formations. More specifically, the present invention relates to a method and apparatus of excavating using a self-contained system disposable within a wellbore. The present invention involves a method and apparatus for excavating using ultra-high pressure fluids. Though the subject invention has many uses, one of its primary uses is to perforate a well and/or stimulate production in that well.
2. Description of Related Art
Wellbores for use in subterranean extraction of hydrocarbons generally comprise a primary section running in a substantial vertical direction along its length. Secondary wellbores may be formed from the primary wellbore into the subterranean rock formation surrounding the primary wellbore. The secondary wellbores are usually formed to enhance the hydrocarbon production of the primary wellbore and can be excavated just after formation of the primary wellbore. Alternatively, secondary wellbores can be made after the primary wellbore has been in use for some time. Typically the secondary wellbores have a smaller diameter than that of the primary wellbores and are often formed in a substantially horizontal orientation.
In order to excavate a secondary wellbore, numerous devices have been developed for lateral or horizontal drilling within a primary wellbore. Many of these devices include a means for diverting a drill bit from a vertical to a horizontal direction. These means include shoes or whipstocks that are disposed within the wellbore for deflecting the drilling means into the formation surrounding the primary wellbore. Deflecting the drilling means can enable the formation of a secondary wellbore that extends from the primary wellbore into the surrounding formation. Examples of these devices can be found in Buckman, U.S. Pat. No. 6,263,984, McLeod et al., U.S. Pat. No. 6,189,629, Trueman et al., U.S. Pat. No. 6,470,978, Hataway U.S. Pat. No. 5,553,680, Landers, U.S. Pat. No. 6,25,949, Wilkes, Jr. et al., U.S. Pat. No. 5,255,750, McCune et al., U.S. Pat. No. 2,778,603, Bull et al., U.S. Pat. No. 3,958,649, and Johnson, U.S. Pat. No. 5,944,123. One of the drawbacks of utilizing a diverting means within the wellbore however is that the extra step of adding such means within the wellbore can have a significant impact on the expense of such a drilling operation.
Other devices for forming secondary wellbores include mechanical/hydraulic devices for urging a drill bit through well casing, mechanical locators, and a tubing bending apparatus. Examples of these devices can be found in Mazorow et al., U.S. Pat. No. 6,578,636, Gipson, U.S. Pat. No. 5,439,066, Allarie et al., U.S. Pat. No. 6,167,968, and Sallwasser et al., U.S. Pat. No. 5,687,806. Shortcomings of the mechanical drilling devices include the limited dimensions of any secondary wellbores that may be formed with these devices. Drawbacks of excavating devices having mechanical locators and/or tubing bending include the diminished drilling rate capabilities of those devices. Therefore, there exists a need for a device and method for excavating secondary wellbores, where the excavation process can be performed in a single step and without the need for positioning diverting devices within a wellbore previous to excavating. There also exists a need for a device that can efficiently produce secondary wellbores at an acceptable rate of operation.